Wife of Humayun's youth, captured at Chausa
Gulbadan's biographical appendix (compiled by Annette Beveridge from Gulbadan-nama and other Mughal-era sources) records that "Bega married Humayun, her first cousin, and she was the wife of his youth. It is out of harmony with the custom of his house that his chief wife should be of less than royal descent" (p. 218). A daughter, 'Aqiqa, was lost when Bega was captured at Chausa.
She was captured at Chausa by Shir Khan, where 'Aqiqa was lost. The appendix notes a naming quirk of the sources: "The historians all call her Haji Begam in recording her capture; it is only Gul-badan who calls her Bega Begam" (p. 219). Why she carries the title Haji Begam at all is treated by Beveridge's appendix as an open, unresolved puzzle: "one thing raises the question whether this was her first pilgrimage, viz., the fact that all the sources, except Gul-badan's, call her Haji Begam... Why is she singled out to bear this title?" — the appendix raises, without resolving, the question, noting only that "in both these cases a renewed pilgrimage might serve as the explanation of the distinction" (p. 220).
Built her husband's tomb
The appendix states plainly: "After this she built her husband's tomb near Dihli, and became its faithful attendant" (p. 220) — no construction dates or cost are given on this page, and no source cited here carries those figures (see gaps).
Beveridge records that "Akbar is said to have been much attached to her, and she was to him like a second mother." "Bega Begam died in 989H. (1581), shortly before Gul-badan's return from Makka. She had almost certainly passed her seventieth year, and was perhaps still older" (p. 220).